1. Field of the Invention
This invention relates to a method of laser emission spectroscopical analysis and an apparatus therefor, and more particularly to improvements in a method of laser emission spectroscopical analysis and an apparatus therefor, wherein a light emitted from the surface of a sample when a laser beam irradiates the surface of the sample is spectroscopically analyzed, and which are suitable for use in direct analysis of hot metal, molten steel, slag and the like.
2. Description of the Prior Art
With the progress of the laser technique, in various fields, there have been attempts to use lasers as a source of excitation to conduct an emission spectroscopical analysis. More specifically, when a powerful laser beam adapted to be focused on the surface of a sample by a focusing lens having a suitable focal length irradiates the surface of the sample, a surface layer of the sample is rapidly heated. Particularly, if the laser beam is formed into pulse shapes of several ten nanosecond, then such conditions occur that energy is locally poured into the sample before heat is diffused in the sample, whereby melting and evaporation occur. Vapor is further excited by the laser beam to be formed into plasma which emitts a light. According to the method of laser emission spectroscopical analysis, this light is transmitted to a spectroscope by means of a suitable light introducing system, spectrally separated by a diffraction grating and the like and formed into spectra, and thereafter, detected by a photographic film, a photomultiplier tube, a photo-diode and the like, whereby contents of aimed elements are determined. This method has such outstanding characteristic features that the method is also applicable to non-electrically conductive materials, can make analysis in atmosphere and so on. However, the method has disadvantages insofar as variations in data are high and the accuracy of analysis is unsatisfactory. The major cause is generally considered to reside in the variations in the output intensity of the laser, with the result that such a method has been normally adopted that the intensity of laser is constantly monitored by a suitable method and data are normally collected only within a predetermined range. However, this method has been disadvantageous in that it is impossible to cope with changes in the distribution of the intensities of laser beams and the adverse influence of the variations in the evaporation and excitation processes due to the contour of the surface of the sample and also due to the presence of contaminations, an oxide layer and the like cannot be removed.